1. Field of the Invention
The invention relates to liquid filtration systems and, more particularly, relates to a liquid filtration capable of ascertaining whether or not a properly-configured filter cartridge is installed in the system. The invention additionally relates to a replaceable filter cartridge which is usable in such a system and which transmits a filter cartridge presence confirmation signal.
2. Discussion of the Related Art
Reliable liquid flow measurement is important in many applications including the beverage handling industry, the pharmaceutical industry, the photo-processing industry, and many different liquid filtration industries. One example is the domestic or household potable water filtration industry in which replaceable filter cartridges are used to treat or purify water prior to its use. Typical filter cartridges have a rated useful life in terms of their volumetric capacity. That is, the filtration effectiveness of the carbon block or other filtration media of such cartridges decreases as the aggregate volume of treated water increases. Typical filter cartridges have a rated life of 500 gallons to 2000 gallons. Failure to replace filter cartridges at the end of their rated lives may result in reduction of treated water quality. Knowing or even estimating the time at which that a filter cartridge's volumetric capacity is reached can be difficult in most households because several different people use different amounts of water without informing one another of the volumes of water used by each.
The need therefore exists to monitor volumetric liquid flow through systems or possibly other parameters relating to liquid flow such as flow rate, and this need is especially evident with respect to the flow of water through a domestic or household type potable water filtration system. However, commercially-acceptably liquid flow meters heretofore have been unavailable for several reasons. First, flow meters tended to be relatively expensive. Second, they have tended to be relatively bulky and difficult to incorporate into existing filtration system designs. Third, and most importantly from the standpoint of regulatory agencies and others who demand accurate flow measurement through relatively wide ranges of source pressures and liquid flow rates, they must be accurate. However, accurate volumetric flow measurement over relatively wide ranges of source flow rates is a difficult task, particularly at medium to low flow rates of 1 gallon per minute or less and is especially difficult at low flow rates of 0.4 gallons per minute or less.
One attempt to design a flow monitor that meets at least some of the criteria described above is disclosed in U.S. Pat. No. 5,540,107 to Silverman et al. (the Silverman patent). The flow meter or flow monitor disclosed in the Silverman patent monitors rotation of a paddle wheel. Specifically, it counts paddle wheel revolutions, then determines aggregate volumetric liquid flow based upon precalibrated data representative of volumetric flow per pulse. This data is used in conjunction with a pre-stored rated volumetric filter cartridge capacity to provide an indication that the filter cartridge associated with the flow monitor requires replacement when the cartridge's volumetric capacity is reached.
The flow monitor of the Silverman patent attempts to minimize pressure drop through an acceptable range of operating flow rates. It includes a housing presenting an impeller chamber in which is disposed an impeller or paddle wheel that essentially acts as a paddle wheel. That is, water enters the impeller chamber peripherally at a first portion, engages the fins or vanes of the paddle wheel to drive the paddle wheel to rotate as the water flows through the impeller chamber, and then exists the impeller chamber radially or at least peripherally at another location. A magnet is inserted into the paddle wheel, and a sensor having an induction coil and a flux concentrator is disposed adjacent the paddle wheel so that the sensor counts two pulses with each rotation of the paddle wheel. The counted pulses can then be used to determine volumetric liquid flow.
The flow meter disclosed in the Silverman patent exhibits several drawbacks and disadvantages.
For instance, both its paddle wheel design and its associated detector require significant torque to move or drive the paddle wheel. Significant torque is required to drive the paddle wheel because the paddle wheel presents significant resistance to the generally peripheral flow of water therethrough. Additional resistance to liquid flow through the paddle wheel occurs because the paddle wheel floats in the paddle wheel chamber and is only loosely or roughly supported. The discrete magnets and induction coil-type detector also provide significant resistance to paddle wheel movement. If left uncompensated for, the pressure drops resulting from these resistances would reduce the liquid flow rate through the flow meter by an unacceptable magnitude.
The Silverman patent was cognizant of the need to minimize pressure drops and, hence, designed features into its flow meter to reduce back pressure. Most notably, it provides a tapered inlet nozzle which directs liquid into the impeller chamber at a direction tangent to the fins or blades of the paddle wheel to increase liquid flow rates. However, by converting the potential energy of the flowing liquid to kinetic energy by accelerating the liquid prior to its entry into the paddle wheel, Silverman's nozzle necessarily increases pressure drop in its flow meter. Moreover, in order to permit the tapered nozzle to operate effectively, an inlet plenum or reservoir must be formed in the housing upstream of the nozzle. Provision of the nozzle and the plenum necessarily complicates the flow meter design and proves only partially effective in reducing pressure drop. In addition, the overall design has a somewhat limited range of linearity (i.e., a flow rate range in which a uniform number of pulses are counted for each gallon of liquid flowing through the meter).
The Silverman patent also recognizes that problems are associated with the use of a discrete magnet and states that it would be preferable to have the paddle wheel as a whole magnetic. However, Silverman considered regulatory constraints on materials, an insurmountable obstacle to this task. (It is believed that the regulatory constraints referenced in the Silverman patent are those that would prohibit the use of a paddle wheel in which materials from the magnet leach or are washed into the water.) These problems are exacerbated by Silverman's paddle-wheel design because Silverman's paddle wheel lacks bearings. Therefore, friction between the magnetic paddle wheel and its support tend to abrade the paddle wheel and cause some of the magnetic materials to rub off into the treated water stream. The Silverman patent therefore requires that the magnet be a separate insert imbedded in the paddle wheel.
In addition, the complexity of the flow meter disclosed in the Silverman patent renders it unduly bulky for many applications. It simply cannot be worked into many existing filter assembly designs without significantly modifying the assembly's design.
Moreover, the configuration of the paddle wheel magnet and the induction coil-type detector impose power restraints on the system that require the use of an external AC power source and an AC to DC converter if the flow meter is to be used to monitor liquids flowing at more than 3 gallons per minute. These power restraints limit the practical applicability of the flow meter disclosed in the Silverman patent to applications in which liquids flowing at less than three gallons per minute are monitored.
Another problem associated with many filtration systems, and even filtration systems having flow monitors and capacity indicators, is that they cannot assure that a spent filter cartridge will be replaced with one properly designed or configured for use in the filtration system or is in place at all. Filter assemblies of most filtration systems will accept any replacement filter cartridge that is of generally the same dimensions as the spent cartridge and that has a post or other coupling member capable of sealingly engaging the mating socket or other coupling member of the base or head of the filter assembly. This design is advantageous to the extent that it permits the use of semi-universal cartridge-to-base configurations. However, this design is disadvantageous to the extent that it cannot guarantee the replacement of a spent filter cartridge with a replacement filter cartridge having the same or generally the same filtration characteristics as the spent cartridge. Hence, a filter cartridge having a granulated carbon filtration medium could be replaced by a filter cartridge having a membranous filtration medium with a resultant change in filtration capability. Similarly, a filter cartridge having a relatively high filtration capacity of, e.g., 2,000 gallons could be replaced by a similarly-dimensioned filter cartridge having a lower capacity of, e.g., 1,000 gallons. If the associated liquid filtration system has a flow meter that generates and displays a REPLACE CARTRIDGE or similar signal only when the 2,000 gallon filtration limit is approached, the REPLACE CARTRIDGE signal will not be generated or displayed until well after the replacement cartridge is actually spent. The need has therefore arisen to provide a filter cartridge for a filter assembly that is capable of providing an indication that the filter cartridge is properly configured for use with that filter assembly.
Another problem associated with filter cartridge replacement in filtration systems having flow monitors is the need for manual reset. That is, a flow monitor may have one or more counters permitting the calculation and/or display of information concerning the aggregate volume of product that has been treated since cartridge installation, the elapsed time since cartridge installation, etc. If the flow monitor is to operate properly, the counter(s) must be reset upon each proper cartridge replacement operation. It would be advantageous if this reset were to occur automatically.